Method and device for locating and identifying objects by means of an encoded transponder

Abstract

A method and device for locating and identifying objects uses an encoding transponder in combination with the use of an SAR device carried in aircraft and spacecraft. Signals transmitted by the SAR device are received by the transponder are provided with an additional dominant signal structure and subsequently retransmitted back to the SAR device. Once the modulated code sequence is known, a signal correlation can be carried out between the signals output by the transponder and the signal reflected from the environment.

What is claimed is: 
     
       1. A device for locating and identifying objects with an SAR device carried in aircraft and spacecraft, comprising: an encoding transponder for use in combination with the SAR device;   means for sending signals from the SAR device to the transponder;   means for providing an additional dominant signal structure to the signals received by the transponder; and   means for subsequently retransmitting the signals back to the SAR device; wherein   the transponder includes a receiving part, a transmitting part, and a modulation part therebetween;   the receiving part includes a receiving antenna (A E ), an amplifier (1), a band-pass filter (2), a first mixer (3), a damping element (4), an intermediate-frequency band-pass filter (5), and a second amplifier (6);   the transmitting part includes a transmitting antenna (A S ), one fixed attenuator (15), one variable attenuator (16), a second mixer (17), a third amplifier (18), a further attenuator (19), and a further band-pass filter (20); and   the modulation part includes a splitter (7), a detector (8) following the splitter, an operational amplifier (9), a monoflop (10), a clock pulse display (11) formed by a D-flip-flop, a code generator (12) following the clock pulse display, a symmetrizing unit (13), and a ring mixer (14); and wherein   the transponder includes at least one integrated or external synthesizer (22) between the first mixer (3) in the receiving part and the second mixer (17) in the transmitting part.   
     
     
       2. A method for locating and identifying objects with an SAR device carried in aircraft or spacecraft, the method comprising: encoding SAR signals with a signal modulation in the SAR device;   sending the signals from the SAR device to the transponder;   encoding the signals received by the transponder with an inverse signal modulation in the transponder;   amplifying the signals prior to transmitting the signals back to the SAR device; and   subsequently retransmitting the signals back to the SAR device;   whereby the transponder is invisible on a SAR image.   
     
     
       3. The method according to claim 2, wherein the signal modulation comprises chirp modulation and the inverse signal modulation comprises inverse chirp modulation, whereby an upward chirp is converted into a downward chirp, and a downward chirp is converted into an upward chirp. 
     
     
       4. The method according to claim 3, wherein the inverse chirp modulation uses various mixed frequencies in transmitting and receiving parts of the transponder. 
     
     
       5. The method according to claim 2, wherein the signal modulation destroys phase information. 
     
     
       6. The method according to claim 5, wherein the signal modulation further comprises additional dominant signal structure. 
     
     
       7. The method according to claim 2, wherein the signal modulation comprises distance modulation and includes no Doppler modulation.